Generic Thermal Sysfs driver How To
===================================
Written by Sujith Thomas , Zhang Rui
Updated: 2 January 2008
Copyright (c) 2008 Intel Corporation
0. Introduction
The generic thermal sysfs provides a set of interfaces for thermal zone
devices (sensors) and thermal cooling devices (fan, processor...) to register
with the thermal management solution and to be a part of it.
This how-to focuses on enabling new thermal zone and cooling devices to
participate in thermal management.
This solution is platform independent and any type of thermal zone devices
and cooling devices should be able to make use of the infrastructure.
The main task of the thermal sysfs driver is to expose thermal zone attributes
as well as cooling device attributes to the user space.
An intelligent thermal management application can make decisions based on
inputs from thermal zone attributes (the current temperature and trip point
temperature) and throttle appropriate devices.
[0-*] denotes any positive number starting from 0
[1-*] denotes any positive number starting from 1
1. thermal sysfs driver interface functions
1.1 thermal zone device interface
1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *type,
int trips, int mask, void *devdata,
struct thermal_zone_device_ops *ops,
const struct thermal_zone_params *tzp,
int passive_delay, int polling_delay))
This interface function adds a new thermal zone device (sensor) to
/sys/class/thermal folder as thermal_zone[0-*]. It tries to bind all the
thermal cooling devices registered at the same time.
type: the thermal zone type.
trips: the total number of trip points this thermal zone supports.
mask: Bit string: If 'n'th bit is set, then trip point 'n' is writeable.
devdata: device private data
ops: thermal zone device call-backs.
.bind: bind the thermal zone device with a thermal cooling device.
.unbind: unbind the thermal zone device with a thermal cooling device.
.get_temp: get the current temperature of the thermal zone.
.set_trips: set the trip points window. Whenever the current temperature
is updated, the trip points immediately below and above the
current temperature are found.
.get_mode: get the current mode (enabled/disabled) of the thermal zone.
- "enabled" means the kernel thermal management is enabled.
- "disabled" will prevent kernel thermal driver action upon trip points
so that user applications can take charge of thermal management.
.set_mode: set the mode (enabled/disabled) of the thermal zone.
.get_trip_type: get the type of certain trip point.
.get_trip_temp: get the temperature above which the certain trip point
will be fired.
.set_emul_temp: set the emulation temperature which helps in debugging
different threshold temperature points.
tzp: thermal zone platform parameters.
passive_delay: number of milliseconds to wait between polls when
performing passive cooling.
polling_delay: number of milliseconds to wait between polls when checking
whether trip points have been crossed (0 for interrupt driven systems).
1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
This interface function removes the thermal zone device.
It deletes the corresponding entry from /sys/class/thermal folder and
unbinds all the thermal cooling devices it uses.
1.1.3 struct thermal_zone_device *thermal_zone_of_sensor_register(
struct device *dev, int sensor_id, void *data,
const struct thermal_zone_of_device_ops *ops)
This interface adds a new sensor to a DT thermal zone.
This function will search the list of thermal zones described in
device tree and look for the zone that refer to the sensor device
pointed by dev->of_node as temperature providers. For the zone
pointing to the sensor node, the sensor will be added to the DT
thermal zone device.
The parameters for this interface are:
dev: Device node of sensor containing valid node pointer in
dev->of_node.
sensor_id: a sensor identifier, in case the sensor IP has more
than one sensors
data: a private pointer (owned by the caller) that will be
passed back, when a temperature reading is needed.
ops: struct thermal_zone_of_device_ops *.
get_temp: a pointer to a function that reads the
sensor temperature. This is mandatory
callback provided by sensor driver.
set_trips: a pointer to a function that sets a
temperature window. When this window is
left the driver must inform the thermal
core via thermal_zone_device_update.
get_trend: a pointer to a function that reads the
sensor temperature trend.
set_emul_temp: a pointer to a function that sets
sensor emulated temperature.
The thermal zone temperature is provided by the get_temp() function
pointer of thermal_zone_of_device_ops. When called, it will
have the private pointer @data back.
It returns error pointer if fails otherwise valid thermal zone device
handle. Caller should check the return handle with IS_ERR() for finding
whether success or not.
1.1.4 void thermal_zone_of_sensor_unregister(struct device *dev,
struct thermal_zone_device *tzd)
This interface unregisters a sensor from a DT thermal zone which was
successfully added by interface thermal_zone_of_sensor_register().
This function removes the sensor callbacks and private data from the
thermal zone device registered with thermal_zone_of_sensor_register()
interface. It will also silent the zone by remove the .get_temp() and
get_trend() thermal zone device callbacks.
1.1.5 struct thermal_zone_device *devm_thermal_zone_of_sensor_register(
struct device *dev, int sensor_id,
void *data, const struct thermal_zone_of_device_ops *ops)
This interface is resource managed version of
thermal_zone_of_sensor_register().
All details of thermal_zone_of_sensor_register() described in
section 1.1.3 is applicable here.
The benefit of using this interface to register sensor is that it
is not require to explicitly call thermal_zone_of_sensor_unregister()
in error path or during driver unbinding as this is done by driver
resource manager.
1.1.6 void devm_thermal_zone_of_sensor_unregister(struct device *dev,
struct thermal_zone_device *tzd)
This interface is resource managed version of
thermal_zone_of_sensor_unregister().
All details of thermal_zone_of_sensor_unregister() described in
section 1.1.4 is applicable here.
Normally this function will not need to be called and the resource
management code will ensure that the resource is freed.
1.1.7 int thermal_zone_get_slope(struct thermal_zone_device *tz)
This interface is used to read the slope attribute value
for the thermal zone device, which might be useful for platform
drivers for temperature calculations.
1.1.8 int thermal_zone_get_offset(struct thermal_zone_device *tz)
This interface is used to read the offset attribute value
for the thermal zone device, which might be useful for platform
drivers for temperature calculations.
1.2 thermal cooling device interface
1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
void *devdata, struct thermal_cooling_device_ops *)
This interface function adds a new thermal cooling device (fan/processor/...)
to /sys/class/thermal/ folder as cooling_device[0-*]. It tries to bind itself
to all the thermal zone devices registered at the same time.
name: the cooling device name.
devdata: device private data.
ops: thermal cooling devices call-backs.
.get_max_state: get the Maximum throttle state of the cooling device.
.get_cur_state: get the Currently requested throttle state of the cooling device.
.set_cur_state: set the Current throttle state of the cooling device.
1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
This interface function removes the thermal cooling device.
It deletes the corresponding entry from /sys/class/thermal folder and
unbinds itself from all the thermal zone devices using it.
1.3 interface for binding a thermal zone device with a thermal cooling device
1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
int trip, struct thermal_cooling_device *cdev,
unsigned long upper, unsigned long lower, unsigned int weight);
This interface function binds a thermal cooling device to a particular trip
point of a thermal zone device.
This function is usually called in the thermal zone device .bind callback.
tz: the thermal zone device
cdev: thermal cooling device
trip: indicates which trip point in this thermal zone the cooling device
is associated with.
upper:the Maximum cooling state for this trip point.
THERMAL_NO_LIMIT means no upper limit,
and the cooling device can be in max_state.
lower:the Minimum cooling state can be used for this trip point.
THERMAL_NO_LIMIT means no lower limit,
and the cooling device can be in cooling state 0.
weight: the influence of this cooling device in this thermal
zone. See 1.4.1 below for more information.
1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
int trip, struct thermal_cooling_device *cdev);
This interface function unbinds a thermal cooling device from a particular
trip point of a thermal zone device. This function is usually called in
the thermal zone device .unbind callback.
tz: the thermal zone device
cdev: thermal cooling device
trip: indicates which trip point in this thermal zone the cooling device
is associated with.
1.4 Thermal Zone Parameters
1.4.1 struct thermal_bind_params
This structure defines the following parameters that are used to bind
a zone with a cooling device for a particular trip point.
.cdev: The cooling device pointer
.weight: The 'influence' of a particular cooling device on this
zone. This is relative to the rest of the cooling
devices. For example, if all cooling devices have a
weight of 1, then they all contribute the same. You can
use percentages if you want, but it's not mandatory. A
weight of 0 means that this cooling device doesn't
contribute to the cooling of this zone unless all cooling
devices have a weight of 0. If all weights are 0, then
they all contribute the same.
.trip_mask:This is a bit mask that gives the binding relation between
this thermal zone and cdev, for a particular trip point.
If nth bit is set, then the cdev and thermal zone are bound
for trip point n.
.binding_limits: This is an array of cooling state limits. Must have
exactly 2 * thermal_zone.number_of_trip_points. It is an
array consisting of tuples of
state limits. Each trip will be associated with one state
limit tuple when binding. A NULL pointer means
on all trips.
These limits are used when binding a cdev to a trip point.
.match: This call back returns success(0) if the 'tz and cdev' need to
be bound, as per platform data.
1.4.2 struct thermal_zone_params
This structure defines the platform level parameters for a thermal zone.
This data, for each thermal zone should come from the platform layer.
This is an optional feature where some platforms can choose not to
provide this data.
.governor_name: Name of the thermal governor used for this zone
.no_hwmon: a boolean to indicate if the thermal to hwmon sysfs interface
is required. when no_hwmon == false, a hwmon sysfs interface
will be created. when no_hwmon == true, nothing will be done.
In case the thermal_zone_params is NULL, the hwmon interface
will be created (for backward compatibility).
.num_tbps: Number of thermal_bind_params entries for this zone
.tbp: thermal_bind_params entries
2. sysfs attributes structure
RO read only value
RW read/write value
Thermal sysfs attributes will be represented under /sys/class/thermal.
Hwmon sysfs I/F extension is also available under /sys/class/hwmon
if hwmon is compiled in or built as a module.
Thermal zone device sys I/F, created once it's registered:
/sys/class/thermal/thermal_zone[0-*]:
|---type: Type of the thermal zone
|---temp: Current temperature
|---mode: Working mode of the thermal zone
|---policy: Thermal governor used for this zone
|---available_policies: Available thermal governors for this zone
|---trip_point_[0-*]_temp: Trip point temperature
|---trip_point_[0-*]_type: Trip point type
|---trip_point_[0-*]_hyst: Hysteresis value for this trip point
|---emul_temp: Emulated temperature set node
|---sustainable_power: Sustainable dissipatable power
|---k_po: Proportional term during temperature overshoot
|---k_pu: Proportional term during temperature undershoot
|---k_i: PID's integral term in the power allocator gov
|---k_d: PID's derivative term in the power allocator
|---integral_cutoff: Offset above which errors are accumulated
|---slope: Slope constant applied as linear extrapolation
|---offset: Offset constant applied as linear extrapolation
Thermal cooling device sys I/F, created once it's registered:
/sys/class/thermal/cooling_device[0-*]:
|---type: Type of the cooling device(processor/fan/...)
|---max_state: Maximum cooling state of the cooling device
|---cur_state: Current cooling state of the cooling device
Then next two dynamic attributes are created/removed in pairs. They represent
the relationship between a thermal zone and its associated cooling device.
They are created/removed for each successful execution of
thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device.
/sys/class/thermal/thermal_zone[0-*]:
|---cdev[0-*]: [0-*]th cooling device in current thermal zone
|---cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
|---cdev[0-*]_weight: Influence of the cooling device in
this thermal zone
Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
the generic thermal driver also creates a hwmon sysfs I/F for each _type_
of thermal zone device. E.g. the generic thermal driver registers one hwmon
class device and build the associated hwmon sysfs I/F for all the registered
ACPI thermal zones.
/sys/class/hwmon/hwmon[0-*]:
|---name: The type of the thermal zone devices
|---temp[1-*]_input: The current temperature of thermal zone [1-*]
|---temp[1-*]_critical: The critical trip point of thermal zone [1-*]
Please read Documentation/hwmon/sysfs-interface for additional information.
***************************
* Thermal zone attributes *
***************************
type
Strings which represent the thermal zone type.
This is given by thermal zone driver as part of registration.
E.g: "acpitz" indicates it's an ACPI thermal device.
In order to keep it consistent with hwmon sys attribute; this should
be a short, lowercase string, not containing spaces nor dashes.
RO, Required
temp
Current temperature as reported by thermal zone (sensor).
Unit: millidegree Celsius
RO, Required
mode
One of the predefined values in [enabled, disabled].
This file gives information about the algorithm that is currently
managing the thermal zone. It can be either default kernel based
algorithm or user space application.
enabled = enable Kernel Thermal management.
disabled = Preventing kernel thermal zone driver actions upon
trip points so that user application can take full
charge of the thermal management.
RW, Optional
policy
One of the various thermal governors used for a particular zone.
RW, Required
available_policies
Available thermal governors which can be used for a particular zone.
RO, Required
trip_point_[0-*]_temp
The temperature above which trip point will be fired.
Unit: millidegree Celsius
RO, Optional
trip_point_[0-*]_type
Strings which indicate the type of the trip point.
E.g. it can be one of critical, hot, passive, active[0-*] for ACPI
thermal zone.
RO, Optional
trip_point_[0-*]_hyst
The hysteresis value for a trip point, represented as an integer
Unit: Celsius
RW, Optional
cdev[0-*]
Sysfs link to the thermal cooling device node where the sys I/F
for cooling device throttling control represents.
RO, Optional
cdev[0-*]_trip_point
The trip point in this thermal zone which cdev[0-*] is associated
with; -1 means the cooling device is not associated with any trip
point.
RO, Optional
cdev[0-*]_weight
The influence of cdev[0-*] in this thermal zone. This value
is relative to the rest of cooling devices in the thermal
zone. For example, if a cooling device has a weight double
than that of other, it's twice as effective in cooling the
thermal zone.
RW, Optional
passive
Attribute is only present for zones in which the passive cooling
policy is not supported by native thermal driver. Default is zero
and can be set to a temperature (in millidegrees) to enable a
passive trip point for the zone. Activation is done by polling with
an interval of 1 second.
Unit: millidegrees Celsius
Valid values: 0 (disabled) or greater than 1000
RW, Optional
emul_temp
Interface to set the emulated temperature method in thermal zone
(sensor). After setting this temperature, the thermal zone may pass
this temperature to platform emulation function if registered or
cache it locally. This is useful in debugging different temperature
threshold and its associated cooling action. This is write only node
and writing 0 on this node should disable emulation.
Unit: millidegree Celsius
WO, Optional
WARNING: Be careful while enabling this option on production systems,
because userland can easily disable the thermal policy by simply
flooding this sysfs node with low temperature values.
sustainable_power
An estimate of the sustained power that can be dissipated by
the thermal zone. Used by the power allocator governor. For
more information see Documentation/thermal/power_allocator.txt
Unit: milliwatts
RW, Optional
k_po
The proportional term of the power allocator governor's PID
controller during temperature overshoot. Temperature overshoot
is when the current temperature is above the "desired
temperature" trip point. For more information see
Documentation/thermal/power_allocator.txt
RW, Optional
k_pu
The proportional term of the power allocator governor's PID
controller during temperature undershoot. Temperature undershoot
is when the current temperature is below the "desired
temperature" trip point. For more information see
Documentation/thermal/power_allocator.txt
RW, Optional
k_i
The integral term of the power allocator governor's PID
controller. This term allows the PID controller to compensate
for long term drift. For more information see
Documentation/thermal/power_allocator.txt
RW, Optional
k_d
The derivative term of the power allocator governor's PID
controller. For more information see
Documentation/thermal/power_allocator.txt
RW, Optional
integral_cutoff
Temperature offset from the desired temperature trip point
above which the integral term of the power allocator
governor's PID controller starts accumulating errors. For
example, if integral_cutoff is 0, then the integral term only
accumulates error when temperature is above the desired
temperature trip point. For more information see
Documentation/thermal/power_allocator.txt
Unit: millidegree Celsius
RW, Optional
slope
The slope constant used in a linear extrapolation model
to determine a hotspot temperature based off the sensor's
raw readings. It is up to the device driver to determine
the usage of these values.
RW, Optional
offset
The offset constant used in a linear extrapolation model
to determine a hotspot temperature based off the sensor's
raw readings. It is up to the device driver to determine
the usage of these values.
RW, Optional
*****************************
* Cooling device attributes *
*****************************
type
String which represents the type of device, e.g:
- for generic ACPI: should be "Fan", "Processor" or "LCD"
- for memory controller device on intel_menlow platform:
should be "Memory controller".
RO, Required
max_state
The maximum permissible cooling state of this cooling device.
RO, Required
cur_state
The current cooling state of this cooling device.
The value can any integer numbers between 0 and max_state:
- cur_state == 0 means no cooling
- cur_state == max_state means the maximum cooling.
RW, Required
3. A simple implementation
ACPI thermal zone may support multiple trip points like critical, hot,
passive, active. If an ACPI thermal zone supports critical, passive,
active[0] and active[1] at the same time, it may register itself as a
thermal_zone_device (thermal_zone1) with 4 trip points in all.
It has one processor and one fan, which are both registered as
thermal_cooling_device. Both are considered to have the same
effectiveness in cooling the thermal zone.
If the processor is listed in _PSL method, and the fan is listed in _AL0
method, the sys I/F structure will be built like this:
/sys/class/thermal:
|thermal_zone1:
|---type: acpitz
|---temp: 37000
|---mode: enabled
|---policy: step_wise
|---available_policies: step_wise fair_share
|---trip_point_0_temp: 100000
|---trip_point_0_type: critical
|---trip_point_1_temp: 80000
|---trip_point_1_type: passive
|---trip_point_2_temp: 70000
|---trip_point_2_type: active0
|---trip_point_3_temp: 60000
|---trip_point_3_type: active1
|---cdev0: --->/sys/class/thermal/cooling_device0
|---cdev0_trip_point: 1 /* cdev0 can be used for passive */
|---cdev0_weight: 1024
|---cdev1: --->/sys/class/thermal/cooling_device3
|---cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
|---cdev1_weight: 1024
|cooling_device0:
|---type: Processor
|---max_state: 8
|---cur_state: 0
|cooling_device3:
|---type: Fan
|---max_state: 2
|---cur_state: 0
/sys/class/hwmon:
|hwmon0:
|---name: acpitz
|---temp1_input: 37000
|---temp1_crit: 100000
4. Event Notification
The framework includes a simple notification mechanism, in the form of a
netlink event. Netlink socket initialization is done during the _init_
of the framework. Drivers which intend to use the notification mechanism
just need to call thermal_generate_netlink_event() with two arguments viz
(originator, event). The originator is a pointer to struct thermal_zone_device
from where the event has been originated. An integer which represents the
thermal zone device will be used in the message to identify the zone. The
event will be one of:{THERMAL_AUX0, THERMAL_AUX1, THERMAL_CRITICAL,
THERMAL_DEV_FAULT}. Notification can be sent when the current temperature
crosses any of the configured thresholds.
5. Export Symbol APIs:
5.1: get_tz_trend:
This function returns the trend of a thermal zone, i.e the rate of change
of temperature of the thermal zone. Ideally, the thermal sensor drivers
are supposed to implement the callback. If they don't, the thermal
framework calculated the trend by comparing the previous and the current
temperature values.
5.2:get_thermal_instance:
This function returns the thermal_instance corresponding to a given
{thermal_zone, cooling_device, trip_point} combination. Returns NULL
if such an instance does not exist.
5.3:thermal_notify_framework:
This function handles the trip events from sensor drivers. It starts
throttling the cooling devices according to the policy configured.
For CRITICAL and HOT trip points, this notifies the respective drivers,
and does actual throttling for other trip points i.e ACTIVE and PASSIVE.
The throttling policy is based on the configured platform data; if no
platform data is provided, this uses the step_wise throttling policy.
5.4:thermal_cdev_update:
This function serves as an arbitrator to set the state of a cooling
device. It sets the cooling device to the deepest cooling state if
possible.